Well they both seem to be the same density. And give the same finish. But my daughter was a little upset when I came home with the blue foam instead of pink. But that's all Lowe's had. The funny part was the guy asking me what I needed it for. Hahaha, try explaining that. "Uhh, Yes sir, I need the foam so I can machine out some exhaust duct forms for my F-22 jet." He either would have called the police or asked me a million questions.

The one thing I don't understand about the foam is that it warps as you machine it. Similar to wood that is sanded on one side only. I thought that it would have had a very consistent density and very little to no internal stress. But apparently there is. The new exhaust (blue foam) came out much worse than the old ones (pink foam). The old ones had a single arch warp to them (About 5-6mm at the highest). The new ones are warped up on each end (About 2mm). And then have another warp in the middle of them (About 2mm as well). The odd thing is that they seem to have been machined to the proper thickness along the whole piece. (Checked at known dimensions along duct). So I am not sure where exactly the warping took place. Really weird.

But these are the things we contend with in the imperfect real world. I am hoping I can get up to the LHS early this week to get the epoxy so I can continue. As of now I can only sand and prep the first layer of epoxy. I should only need to apply one more to get good finish. But we shall see. In the mean time I will be working on the wings. Just have to machine out the airfoil patterns and I can hot wire them.

As a side note. I continued working on getting the plans ready. Getting everything annotated and such so everyone can understand them. The drawing is kind of a mess at the moment.

Yeah the heat from machineing warps foam, that's why they use harder materials for plugs! haha And those are just the dimensional twist's you have seen, it flat out shrinks in and out on itself. And there's a good chance it will happen again when you epoxy and cloth them. That rough surface your talking about is the grain, blue,pink, even FF all have a grain that cuts and sands better one way than the other. What I do if I am making a part from foam is either on the ends and or on the flat non shaped back side I will set in thick enough wood to be a spine. This you can use to grab screws to hold it flat, or set to a part board, or dowel to other part. All you have to do for now is use one to mark a part board then combine them and glass, but mark splits in ends so they can be seen. Then glass them together and use part board to pull each end seam 90 degrees to part board ensureing no twist. If that makes sense.

I understand what you mean. Had I thought it out well enough I would have spined the back of the foam with something hard before machining. But I did not expect the odd warping I got this time. The warp on the first ones was very easy to correct so I did not worry about it. I still plan on cutting out some wood templates to epoxy to foam plugs to. Just have to get there. In fact, that was why I started working on the plans again last night. But I got side tracked trying to make the drawing look neater. Oh well.

Hey guys, have a question. Was talking with a friend and tossing around ideas and thoughts on the duct work. And I was wondering if there is a particular reason that no one vacumm forms there ducts from plastic. In my mind this would be a much much simpler method of making them. Along with have a perfectly smooth finished surface. And more than likely, lighter than fiberglass ducts.

I want to get these ducts done yesterday. But I am out of West System's epoxy and don't have the means to get any in short order. Not to mention the fact that I still need another coat on the duct forms before I can start glassing. But the other thought that comes to mind is that it would be easier to vacumm form them if I wanted to make multiples.

But if I were to use the vacumm form method, then I would have to coat the foam forms. A simple coat of minwax polycrylic would probably provide a smooth enough surface.

Thanks for any thoughts, Nick

nem3 any more progress?

ha, I feel like I am moving along at a snails pace. But I don't think they even move as slow as I have been. I have been so wrapped up in my choppers since it has been nice out that I haven't done much of anything since my last update. I did get the plastic so I can try the vacumm forming. But I still need to make the box to do so, as well as a few peices to mount the foam forms to. I already have the G-code made for the stuff I need. Just need to find the time at work to cut them out.

Other than that, I have cleaned up the drawing a little. And have thought about just releasing the plans. But I am not real sure about that. I'd hate to have someone start following them just to find out there is some big mistake I made.

As it looks right now, this project may sit until fall/winter rolls around again. I have been real busy with work, family and the chopper hobby. I feel that if I were to try and work on it, I would end up rushing to get it done before fall. I rushed on the last one and it just ended up over weight, don't want to do that again.

As a side not, I did pick up one of those Phase 3 EF-16's, and stuffed one of my MF480's into it. The jet flies great for what it is, and I am very happy with the end result. Great learning experience!

Thanks, Nick

7 months and I still haven't accomplished anything. And the future looks pretty bleak.

So I thought I would pose a question for those of you that were interested in the plans. If I posted the CAD files that I used to make the parts I have made so far. Would that be enough to get you guys started?

Nem

Would love to do a twin 90mm F-22, but I have my hands full at the moment on my Stumax Typhoon.

I know how these projects can drag on, I have been doing mine for 12months now

BUT, my only advice, if your wife can bear it, is to stick with it.

It will be worth it in the long run!

Chris

Originally Posted by nem3

7 months and I still haven't accomplished anything. And the future looks pretty bleak.

So I thought I would pose a question for those of you that were interested in the plans. If I posted the CAD files that I used to make the parts I have made so far. Would that be enough to get you guys started?

really compliment for your wonderfull work!!

ciao
alberto

Nick,

I am all for it. Your parts would be very helpful to my project. I want to getthis project together and flying.

Tom

Looking for the plans...

Getting warmer

Nick,

Thanks so much for your help. Once I get started with this project I will post some pictures for you. Thanks Again,

Tom

Thanks Nem will be a good project to learn for SW skills : )

Matt

At least 30 downloads so far. Can't wait to see the results

Nem3,

The all the parts came over. I am going to convert the 2D to 3D and assemble them in SW.

Any known fixes needed to be made? Or any areas that you wanted to change?

Matt